1. Field of the Invention
The present invention relates to a gravity-type accelerometer used to calculate the estimated vehicle speed of a motor vehicle, and more particularly to a zero-point correction device there for.
2. Description of the Prior Art
In antilock brake control devices and other wheel behavior control devices, estimating wheel slipping or spinning based on the calculated vehicle speed, and estimating the coefficient of friction between the tire and the road surface are important factors directly affecting the control performance of the device. The coefficient of friction between the tire and road is normally estimated based on the estimated value of vehicle acceleration during control, and the vehicle acceleration is estimated based on the estimated vehicle speed. Therefore, the performance of the wheel behavior control device is greatly dependent upon the precision of vehicle speed estimation.
However, if the vehicle speed is estimated from the wheel speed alone, the estimating precision is reduced significantly when the tires slip or spin badly. Therefore, if the vehicle speed and vehicle acceleration are estimated based on both the wheel speed and the acceleration obtained from a reliable accelerometer, the estimating precision can be significantly increased. A typical type of accelerometer is the gravity-type accelerometer.
As illustrated in FIG. 5, the gravity-type accelerometer detects acceleration by converting the displacement of an weight F caused by acceleration to an electrical signal using resistors, piezoelectric elements, differential transformers, and other devices. But besides the undesirable effects caused by the relatively long-term variations, such as installation precision, electrical drift and gain change, the effect of the slope of the road being drive on is also unavoidable.
Therefore, when using a gravity-type accelerometer, it is extremely important how to correct these undesirable effects including the effect of the slope of the road.